The present invention relates to an electromagnetic relay, and more particularly relates to an electromagnetic relay in which switch contacts are switched over by movement of an armature assembly in response to the energization of an electromagnet, in which no asymmetric reaction force is produced when the device is switched.
There is a known type of electromagnetic relay, which will now be described. An electromagnetic coil is wound on a spool, and the spool is fixedly mounted to a yoke member which has a first end portion at one end of the spool and two end portions at the other end of the spool somewhat spaced apart from one another which constitute magnetic pole pieces. An iron core is inserted through the middle of the spool and is held in place by its one end being crimped to said first end portion of the yoke member; in this position, the other end of said iron core, which constitutes another magnetic pole piece, is held between the pole pieces constituted by said two other end portions of the yoke member, each of which lies to one side of said end of said iron core with a certain gap being defined therebetween. Thus, when the electromagnet is energized, a magnetic circuit is created, and the two pole pieces of the yoke are magnetized to become poles of a particular polarity, for example in the case of energization in a particular direction they become south poles, while the end of the iron core between them is magnetized to become a pole of the opposite polarity, i.e. in this example becomes a north pole. An armature piece is made up by two iron plates being joined together by a plate shaped permanent magnet in approximately a C-shaped configuration, with one of the iron plates being thus magnetized to be a north pole and the other a south pole. This armature piece is positioned with the two iron plates inserted into the aforementioned gaps between the poles defined by said other end portions of the yoke member and the pole defined by said end of said iron core, and is mounted on on a block member which can move from side to side so that the iron plates can move towards and away from said end of said iron core. Contacts are provided which are opened and closed according to said sideways motion of said block member, either directly or via spring pieces which are bent thereby. Depending on the configuration, sideways biasing may be applied to the block member.
Thus, when the coil is energized in said particular direction, the one of the pole pieces which is magnetized to be a north pole by the permanent magnet is attracted to the pole piece of the yoke on its one side and is repelled from the side of the end of the iron core on its other side, while on the other hand the other one of the pole pieces which is magnetized to be a south pole by the permanent magnet is repelled from the pole piece of the yoke on its one side and is attracted to the side of the end of the iron core on its other side; and thereby the block member is biased in a certain sideways direction, and moves so as to open or close certain of its contacts. On the other hand, when the coil is energized in the electrical direction opposite to said particular direction, the one of the pole pieces which is magnetized to be a north pole by the permanent magnet is repelled from the pole piece of the yoke on its one side and is attracted to the side of the end of the iron core on its other side, while on the other hand the other one of the pole pieces which is magnetized to be a south pole by the permanent magnet is attracted to the pole piece of the yoke on its one side and is repelled from the side of the end of the iron core on its other side; and thereby the block member is biased in the opposite sideways direction, and moves so as to close or open said certain of its contacts. (The position when the coil is not energized can be either of these positions or a position intermediate between them, depending on the biasing of the block member). Thereby the contacts are reliably and positively switched, and a good and efficient magnetic circuit with little loss of magnetic flux is provided.
However, this device has a shortcoming, in that the movement of the block member occurs to and fro along a line which is offset from the general center of the device including its center of gravity, which generally passes through or near the center of the electromagnetic coil. Therefore, when the relay performs switching action, an unbalanced and off center jerking force is caused to be applied to the base board such as a printed circuit board to which the relay is fitted, and this off center jerking force creates a jerking torque around the center of gravity the relay. This can give rise to various problems with regard to the fixing of the relay to the printed circuit board, and can mean that after a certain service life the fixing of the relay becomes loosened.
Another disadvantage of the construction outlined above is that, because the one end of the iron core is crimped to said first end portion of the yoke member, the integrity of the magnetic circuit is not perfectly assured. Such crimping, if imperfectly done, can greatly raise the magnetic resistance of the magnetic circuit, thus deteriorating relay performance. Yet in the outlined prior art construction the use of such crimping for fixing the end of the iron core to the yoke member is very much preferable from the point of view of convenience and cost of assembly.
An expedient that might be thought of for curing the above outlined unbalance problem might be to provide two of the relay construction detailed above mounted back to back, so that the two forces due to the movements of their armature assemblies were on opposite sides of their center of gravity and the unbalanced portions thereof canceled one another out; but this would increase the overall size and particularly the length of the device, and would increase its cost substantially. Further, this expedient would not solve the problem that the crimping can deteriorate the quality of the magnetic circuit.